Method for preventing corrosion



Jan. 17, 1967 n. R. ANTHCNY ETAL 3,298,438

I METHOD FOR PREVENTING CORROSION Filed yeb. 20. 1961 2 Sheets-Sheet 1 mrssr L INVENTORS.

2. DONALD R. ANTHONY Mo I y RADO G.LONCARiC ROBERT E. FIELDS Jnn. 17, 1967 i NY ETAL 3,298,438

I METHOD FOR PREVENTING CORROSION I 7 mod Feb. 20. 1961 I 2 Sheets-Sheet 2 ACID GASES VOLUME PERCENT m VAPOR SPACE I m 0 I000 v 2000 a 3000 4000 DEPTH m WELL (FEET) ATTEST IN V EN TOR-S.

DONALD R. ANTHONY BY RADO G. LONCARIG ROBERT E. FIE s L404 .5

United States Patent 3,298,438 METHOD FOR PREVENTING CORROSION Donald R. Anthony, Rado G. Loncaricfand Robert E. Fields, Dallas, Tern, assignorsto'The' Atlantic Refining Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Feb. 20, 1961, Ser. No. 90,527

can s- Clown This invention relates to inhibition of corrosion of metallic surfaces exposed to corrosive vapors." More specifically, this invention covers methods for injecting anhydrous ammonia or normally gaseous amines into the annular vapor space of oil, water and gas wells. In another aspect, this invention pertains to the amount of volatile inhibitor to be usedf In still another aspect, this invention pertains to methods for injecting liquefied normally gaseous inhibitors. i

i; In crude oil and natural gas production, various types of wells are used to either produce the underground fluids or to inject fluids into underground formations.

- Usually, these wells have an outer string of pipe called casing and an inner string of pipe called tubing. Since the tubing is smaller than the casing, there is a space between the two strings which is called the annulus or annular space. Normally, the fluids are flowed inside the tubing and a vapor space is formed in annulus. In many instances, the entire annular space maybe a vapor space and the vapor space, therefore, may'extend I thousands of feet into the ground.""Frequen'tl y, the

fluids flowing in. the well contain water and acid gases like hydrogen sulfide, carbon dioxide or both. the fluids are flowed, water vapors and acid gases collect in the annular vapor space. These gases cause corrosion of the tubing and casing exposed to the corrosive vapors. Various types of corrosion inhibition measures have been proposed to prevent this acid gas corrosion andthe use of volatile inhibitors like ammonia has beer suggested. But, no one has suggested a practical'Qs afe ivay of introducing liquefied normally gaseous inhibitors like arnmonia into this annular space especially when the pressure within the annular space exceeds the vapor pressure of the liquid inhibitor. Nor has anyone suggested effective limits on theamo unt of hiatus t immer to be used in protecting the metal surfaces to thesecorrosive vapors; In addition, the prior art does not teach an effective method of determining the depth of penetration of a volatile inhibitor intothe annular vapor-space. It is highly desirable to have an effective method'of determining the depth of penetration of volatile inhibitors when the inhibitor is to be used in the vapor space of wells since theoretical calculations indicate that'this inhibitor if injected at the surface will not readily diliuse through a long, narrow cylindrical area: iike that formed by the annular vapor space. s

For the most part, moreover, prior art practices utilizing volatile inhibitors are designed for vapor zones where the pressure is below the yapor pressure pine liquid inhibitor and the inhibitor is added in its yaporized state or in some reacted form. These systems are impractical for high pressure equipment Even in lowpressure wells,

moreover, it is undesirable to leave containers containing liquefied normally gaseous inhibitors unprotected at the wellhead since many of these inhibitors are highly toxic. In addition, whenever a lar'ge number of separate units are used to handle toxic materials and' untrained personnel may be involved, the hazards are increased manyfold. It is, therefore, desirable to have a portable system for introducing the volatile inhibitor into not only high pressure systems but into low pressure systems as well. It is desirable that the injection equipment be portable 3,298,438 Eateni'ed Jan. li, 1967 and designed to protect personnel from the hazards of handling toxic materials; Such equipment, moreover, should be capable of metering the amount of inhibitor used and lend itself to use with commercially available containers. The prior art does not provide equipment of this nature for handling liquefied norm-ally gaseous toxic inhibitors. 7

Accordingly, it is the object of this invention to provide a method for preventing vapor space corrosion regardless of the pressure encountered utilizing liquefied normally gaseous inhibitors. 4 c

It is another object of this invention to provide a method for measuring the eliective depth of penetration of gaseous inhibitors into the annular space of a well bore.

It is still another object of this invention to establish amethod of preventing vapor space corrosion caused by acid gases like carbon dioxide, hydrogen sulfide or both.

Another object is to provide methods for preventing plugging oi lines used in introducing the inhibitor and for purging such lines after use. Another specific object of this invention is to provide such equipment especially suited to injection of liquefied normally gaseous corrosion inhibitors into the annular space of well bores.

For a better understanding of this invention, reference should be had to the accompanying drawings inwhich:

ble injection equipment.

FIGURE 2 is a depth of penetration curve for a typical we ll illustrating theamount of inhibitor required.

FIGURE 3 is a side, elevational view of the equipment utilized in obtaining data for the depth of penetration curve of FIGURE 2. i

This invention relates to inhibition of corrosion of metallic surfaces exposed to corrosive vapors. This invention is divided into three sections with the first section covering methodsior injecting anhydrous ammoniaor normally gaseous amines into the annular vapor space of oil; water and gas wells. The second section pertains to the depth of penetration of the volatile inhibitor into the anhdlar space of well bores and to equipment for measuring the same. The third section sets forth the amount bf volatile inhibitor found necessary for protecting metallic surfaces exposed to'coi'rosiye' acid gases in'the annular vp l w n v r. I

Portable injection equipment The mobile injection equipment is designed to provide a safe, compact unit for injecting pure, volatile, toxic,

liquefied normally gaseous inhibitors into high or low hibitors. The equipment was designed to permitoperation from ground level and the high pressure system is located on' one side of the truck away from the driver and most of the controls used during actual injection of the, inhibitor.

While the injection equipment is suitable for all types of liquefied normally gaseous inhibitors, the following deervoir 11 is cover 13 which permits heating of the liquid inhibitor during cold weather. Inhibitor reservoir 11 is connected by way of flexible hose 15 to manifold valves 17 interconnecting inhibitor reservoir 11 with inhibitor delivery line 19 and venting line 21. The manifold valves are located under the rear end of the truck bed so that the valves are operable from the ground and out of the way of loading and unloading the inhibitor. Moreover, in this position, the manifold valves can be covered and locked to prevent tampering while the unit is not in use.

Venting-line 21 connects all the lines of the injection equipment with vent hose 23 on vent hose reel 25. Vent line 21 and vent hose 23 permit venting and draining of the injection lines to a point remote and downwind of the truck. The end of vent hose 23 is equipped with spikes (not shown) which can be driven into the ground to prevent the end of the hose from whipping.

Inhibitor delivery line 19 passes through insulated box 27 which allows cooling of the inhibitor in delivery line 19 during hot weather. On delivery line 19 is pressure gauge 29 which is used to measure the vapor pressure of the liquid inhibitor. On delivery line 19. after insulated box 27 is sight fiow indicator 31 which has windows on both sides for see-through use to indicate when delivery line 19 is purged and full of liquid inhibitor, when there is flow in the line and when inhibitor reservoir 11 is empty. These features are important since the amount of inhibitor injected is measurable only so long as inhibitor delivery line 19 is full of liquid inhibitor.

Next to flow indicator 31 is two-way plug valve 33. One branch of two-way valve 33 connects with line 35 which in turn is connected to the bottom of storage tank 37. Storage tank 37 acts as a reservoir for a water-miscible'liquid like glycol or alcohol, which liquid is inert to the inhibitor and acts as a purging fluid as hereinafter described. Between storage tank 37 and two-way valve 33 on line 35 are valve 39 and check valve 41. Check valve 41 acts as a safety valve to prevent liquid inhibitor from backing up into storage tank 37.

Storage tank 37 is equipped with sight gauge glass 43, pressure gauge 45 and pressure relief valve 47. Also connected to the top of storage tank 37 is line 49 which communicates with cylinder 51. Cylinder 51 contains an inert gas like helium or nitrogen of sufficient pressure to pressurize storage tank 37 to a pressure above the vapor pressure of the liquid inhibitor.

The second branch of the two-way plug valve 33 is connected to pump intake line 53 which in turnleads to inhibitor pump 55 and to vent line 21 by way of valve 57. Two-way plug valve 33, therefore, permits rapid switching from inhibitor to water-miscible fluid or vice versa without stopping inhibitor pump 55. Moreover, since the water-miscible fluid is at a pressure higher than that of the liquid inhibitor, the inhibitor does not vaporize and vapor lock inhibitor pump 55 when two-way valve 33 is used to switch pump intake line 53 from inhibitor to the water-miscible fluid in line 35.

Inhibitor pump 55 can be any suitable adjustable de- -livery pump capable of pumping at pressures exceeding the pressure in the equipment to be treated and capable of pumping at a rate sufficient to overcome vapor-locking tendencies of the liquefied normally gaseous inhibitor. The pump used herein was a duplex, positive displacement, single acting reciprocating plunger type pump with adjustable capacity. Inhibitor pump 55 can be motivated by a power take-off drive which is engaged from inside the truck. The truck engine r.p.m. is measured by a tachometer installed inside the truck. This allows adjusting the truck speed to correlate with the desired pump rate.

On the outlet or high pressure side of inhibitor pump 55 is injection line 59 which has three branches. One branch leads to'pressure relief valve 61 which upon opening discharges the contents of line 59 to vent line 21.

4 Pressure relief valve 61 operates as a safety valve should unusually high pressures be reached in injection line 59.

A second branch of injection line 59 leads to backpressure regulating valve 63 which holds back pressure on the inhibitor in injection line 59 and prevents vaporlocking of inhibitor pump 55. Back-pressure regulating valve 63 also permits the injection equipment to be used for treating equipment with internal pressures below the vapor pressure of the liquid inhibitor.. The valve, there fore, is set at a pressure dependent upon the material being pumped, e.g.,. for ammonia, it is set at 300 p.s.i.g.

The third branch of injection line 59 leads to valve 65 which is used to open by-pass line 67 around back-pressure valve 63. By-pass line 67 also has a branching line leading to valve 69 which upon being opened discharges the contents of by-pass line 67 to vent line 21.

Connected to back-pressure regulating valve 63 andby-pass line 67 is injection hose 71 which is wound around injection hose reel 73. The reel operates with an automatic rewind to facilitate handling of the injection hose. Injection hose 71 is a high pressure hose designed for this particular service.

The outlet end of injection hose 71 is equipped with check valve 75 which prevents high pressure fluids from the equipment being treated from entering the injection equipment. Check valve 75 has a manual by-pass (not shown) used to equalize pressure across the check valve to open the valve should it be closed during operation.

The end of injection hose 71 is also equipped with a quick-connect union (not shown) having a double sealing feature. This allows rapid connection to the equipment to be protected and speeds operation while maintaining safety. a

In operation, the mobile unit is parked from 40 to 50 feet crosswind from the equipment to be treated. Vent hose 23 is unreeled and staked down downwind from the mobile unit. Twoway valve 33 is opened to storage tank 37 containing the water-miscible liquid. All other valves are closed. The connections (not shown) on the equipment to be treated are purged of oxygen by venting some of the gas in the equipment to the atmosphere. Thereafter, injection hose 71 is unreeled and connected to these connections. After connecting injection hosc 71 to the equipment to be treated, one of manifold valves 17 is opened to let liquid inhibitor from inhibitor reservoir 11 fill inhibitor delivery line 19. The operator checks sight-flow indicator 31 to note when the inhibitor delivery line 19 is full of liquid inhibitor. Inhibitor delivery line 19 must be kept full of liquid inhibitor at all times during an injection period. If the liquid vaporizes, the pump will vapor lock. In order to prevent the formation of vapors, it was discovered that the liquid inhibitor in the inhibitor reservoir 11 must be kept at a righer temperature than the liquid inhibitor in inhibitor delivery line 19s It was found that this temperature differentialcould be maintained by cooling inhibitor delivery line 19 on hotter days and heating inhibitor reservoir 11 on cooler days. To cool inhibitor delivery line 19, insulated box 27 is filled with ice or other refrigerant. To heat inhibitor reservoir 11, the exhaust from the truck can be piped over the reservoir or an electrical heating unit can be installed under cover 13.

After filling delivery line 19 with liquid inhibitor and insuring that the inhibitor will remain liquid, storage tank 37 is pressurized with inert gas from cylinder 51 to a pressure above-the vapor pressure of the liquid inhibitor. This pressure is determinable from pressure gauge 29 in delivery line 19. Valve 39 in line 35 is opened to let water-miscible liquid flow from storage tank 37 through two-way valve 33 to pump intake line 53. The water-miscible liquid is an important feature of the injection process since water collects in the equipment connections and ammonia or volatile amines in the presence of water react with carbon dioxide to form a solid precipitate which may plug the equipment connections. The

water-miscible liquid removes water from these connections.. The water-miscible liquid is also useful in purging oxygen out of .the injection lines. Oxygen accelerates corrosion. The water-miscible liquid is also used to purge the equipment lines of traces of the toxic inhibitor which being hazardous could otherwise cause injury to operating personnel. Another advantage of water-miscible liquid is to insure future free operation of valves. The water-miscible liquid should be inert to the inhibitor and acid gases. hols, and ketones.

Thereafter, the truck engine is set at thedesired r.p.m. The optimum speed is predetermined to fit the type of inhibitor and pump capacity being used. For example, for ammonia, it was found that a speed of 1000 rpm. was optimum for a pump having a capacity of 0.52 gallon per minute at 51.1 strokes per minute. vWhen a constant speed is used, the amount of inhibitor depends solely upon time and, therefore, an accurate means for metering the inhibitor is provided. z a 1' The. pump power takeoff is engaged thereby causing inhibitor pump 55- to pump water-miscible liquid from storage tank 37 until two-way valve 33 is switched to open pump intake line 53 to inhibitor delivery line 19.

. Inhibitor is-pumped for the desired period of time depending upon theamount to be injected.- Immediately thereafter, two-way valve 33 is reswitched. to line 35- and water-miscible liquid is pumped for ,suffi'cient time to purge the injection equipment of the inhibitor.

Depth of penetration of the inhibitor into the annulus of the well i As stated previously, it is highly desirable to havean eifective method of determining the depth ofpenetration of volatile inhibitors into the vapor space i of wells. Basically, the method developed herein comprises bleeding off the gas in. the annular spacev at a measured rate and making periodic measurementsof the inhibitor and acid contents. The equipment utilized in this method is illustrated in FIGURE 3.

The equipment illustrated is designed to flow the; gas out of the annulus as a column at a steadyrate of flow. The equipmentpermits collection of periodic samples of the gas and measurement of. the physical conditions-of the gas-so as tocalculate the depth at which a given sample corresponds. ,Communicating with the vapor space of the annulusof the well is bleed line 77 through which the gas is flowed. Near the well head, connected to bleed line 77, are pressure recorderi79 and. sampling line 81. The flow rate through line 77 is controlled by variable choke valve 83. Downstream of choke valve 83 and connected to. line 77 are,temperaturerecorder 85 and pressure recorder 87. In the end of the line 77 is orificeplate89.

In performing a depth ofpenetration ,test,.thegas is flowed out of the annulus as a column exactlyas it existed in the well bore. In other words, each sample of gas analyzed can eventually be correlated with a certain depth as hereinafter described. The gas flow, therefore, once it is started should notrbe disrupted as this could cause mixing of the gases from various depths and give erroneous measurements. The rate of flow, moreover,.should not be too rapid as this could cause turbulence in well bore and destroy the continuity of the gas column. On the Materials suggested are glycols, alco-- other hand, the rate should not be too slow as this too could result in mixing of the gases from various depths.

In addition, the rate of flow must be at least partially dependent upon the analytical techniques and the number of measurements to be taken. In the procedure used herein, the analytical equipment may include such devices .as a portable chromatograph especially designed for measuring the inhibitor and acid gas contents, an Orsat designed for acid gas measurements to check the chr0- matograph', a Tutwiler apparatus for measuring hydrogen sulfide, a modified Nessler test for inhibitor concentrations below 2 percent, Hydrion pH papers, and lead acetate papers for hydrogen sulfide detection. Based on the above considerations, it was determined that a six hour test would be optimum for a 4000 foot well; therefore,

read on recorder 87. The gas was-flowed continuously for the desired period and samples of the gas were taken approximately every 20 minutes and analyzed for inhibitor, acid gas contents and pH utilizing the analytical equipment mentioned previously. with, the wellhead pressure was recorded by recorder 79 and the gas temperature was recorded by recorder 85. After the desired period, choke 83 was closed and the depth of penetration test discontinued. The results of a depth of penetration test are illustrated in FIGURE 2 in which the analyses are plotted against depth. This figure was determined by standard gas calculations utilizing the pressure-volume-temperature relationships as shown by the recorders and the flow rate as indicated by the pressure drop across orifice89. Since these calculations are well known, it is felt that a more detailed discussion is unnecessary. a

' Criteria for protection An inhibition method for. protecting steel surfaces in the corrosive vapor zone of the annulus of wells utilizing liquefied normally gaseous inhibitors is only practical if anoperable criterion for protection is presented. Of

course, criteria are largely dependent on the type of system involved. For example, the nature of the system usually controls the conditions that can be measured to 'form. parameters for the criterion.

For example, in the vapor spaceof tanks, the inhibitor content adjacent the point of corrosion, can easily be determined. On the' other hand, to measure the inhibitor content at a point thousands of feet in the ground requires expensive tests like those described previously.

The depth of penetration tests mentioned previously have assisted in determining a workable criterion for the added to react with at least one-third of the acid gases to thedesired depth, but results indicate that lesser amounts .will give protection to that depth as long as theamount. of inhibitor used is at least one-fourth of the totaLacid gases present to the desired depth. Upper limits on the amount of inhibitor used are dictated by eco- 4 nomics.

After injecting at least one-fourth of the amount of in- Simultaneously therein the gas at the wellhead throughout the interval between injections. It was found that the rate of downward movement of the inhibitor exceeded the upward movement of the acid gases if the inhibitor concentration is maintained at this level. For example, out of 90 wells tested, most wells could be protected with a 25 pound injection of ammonia every six months and the desired concentration was more than adequately maintained. All indications were that even less amounts of inhibitor are required to maintain this concentration-once the well has been injected with the quantities previously set forth.

The description herein presented has set forth preferred embodiments of methods and apparatus for injecting liquefied normally gaseous inhibitors into both high pressure and low pressure equipment, of methods and apparatus for measuring the depth of penetration of volatile inhibitors into the annular vapor space of wells and of methods for initiating and maintaining protection of steel surfaces exposed to acid gas vapors in the annuli of the wells. It 'will be understood that many modifications and variations may be made in the details hereinber'ore set forth without departing from the scope of this invention which is limited only as defined in the appended claims.

We claim:

1. A method of injecting liquefied normally gaseous corrosion inhibitor into the vapor space of the annulus of a well when the gases in said vapor space contain carbon dioxide which method comprises connecting an inhibitor injection system to an inlet to said vapor space, pumpinga first amount of water-miscible liquid into said inhibitor injection system, said first amount of said water-miscible liquid being at least sutficient to remove water from said inhibitor injection system and said inlet, cooling a liquefied normally gaseous corrosion inhibitor to a temperature sutficient toprevent vaporization of said inhibitor in said injection system, said liquefied normally gaseous corrosion inhibitor characterized by the fact that said inhibitor will react with carbon dioxide and water to form a solid salt, pumping through said inhibitor injection sysof a well when the gases in said vapor space contain carbondioxide, which method comprises connecting an inhibitor injection system to an inlet to said vapor space,

pumping a first amount of water-miscible liquid into said inhibitor injection system, said first amount of said watermiscible liquid being at least sufficient to remove water from said inhibitor injection system and said inlet, heating a liquefied normally gaseous corrosion inhibitor to a temperature sufiicient to prevent vaporization of said inhibitor in said injection system, said liquefied normally gaseous corrosion inhibitor characterized by the fact that References Cited by the Examiner UNITED STATES PATENTS 2,776,714 1/1957 Stanclift et al 16642 2,795,278 6/1957 Battle 1661 2,800,183 7/ 1957 Jenkins 1664 2,815,078 12/1957 Reynolds 1661 2,858,893 11/1958 Waggener 16675 2,884,067 4/1959 Markeu 16675 2,973,811 3/1961 Rogers 166-4 3,038,856 6/1962 Milligan 1661 X OTHER REFERENCES Cragoe, C.S. et a1.: Vapor Pressure of Ammonia, Bureau of Standards Scientific Paper No. 369, vol. 16, 1920- 21, pp. 33, 34and 35 relied on, QC 105.

Menaul, P.A.: Mitigation of Oil Field Corrosion, in World Oil: Production Section pp. 152-153, January 1950.

Muir, P.D.: Organic Inhibitors, in The Oil and Gas Journal. pp. 143-146, February 15, 1954.

- Greenwell, H.E.: et al. Casing Corrosion, in Corrosion, vol. 11, No. 11, pp. 491!- 496t; TA 262 C58.

Jones, LW. et a1.: New Inhibitor Safeguards Vapor Spaces Against H S Corrosion, in The Oil and Gas Journal, Vol.54, Sept. 24, 1956, pp. 132-137, TN 860, 039.

CHARLES E. OCONNELL, Primary Examiner.

R. W. COLLINS, T. A. ZALENSKI, S. J. NOVOSAD,

Assistant Examiners.

Use of Ammonia to Prevent 

1. A METHOD OF INJECTION LIQUEFIED NORMALLY GASEOUS CORROSION INHIBITOR INTO THE VAPOR SPACE OF THE ANNULUS OF A WELL WHEN THE GASES IN SAID VAPOR SPACE CONTAIN CARBON DIOXIDE WHICH METHOD COMPRISES CONNECTING AN INHIBITOR INJECTION SYSTEM TO AN INLET TO SAID VAPOR SPACE, PUMPING A FIRST AMOUNT OF WATER-MISCIBLE LIQUID INTO SAID INHIBITOR INJECTION SYSTEM, SAID FIRST AMOUNT OF SAID WATER-MISCIBLE LIQUID BEING AT LEAST SUFFICIENT TO REMOVE WATER FROM SAID INHIBITOR INJECTION SYSTEM AND SAID INLET, COOLING A LIQUEFIED NORMALLY GSEOUS CORROSION INHIBITOR TO A TEMPERATURE SUFFICIENT TO PREVENT VAPORIZATION OF SAID INHIBITOR IN SAID INJECTION SYSTEM, SAID LIQUEFIED NORMALLY GASEOUS CORROSION INHIBITOR CHARACTERIZED BY THE FACT THAT SAID INHIBITOR WILL REACT WITH CARBON DIOXIDE ND WATER TO FORM A SOLID SALLLT, PUMPING THROUGH SAID INHIBITOR INJECTION SYSTEM A PREDETERMINED AMOUNT OF SAID INHIBITOR, SAID INHIBITOR CONTACTING SAID FIRST AMOUNT OF WATER-MISCIBLE FLUID IN SAID INJECTION SYSTEM, AND PUMPING THROUGH SAID INHIBITOR INJECTION SYSTEM THENCE TO SAID INLET AND TO SAID VAPOR SPACE A SECOND AMOUNT OF WATER-MISCIBLE LIQUID, SAID SECOND AMOUNT CONTACTING SAID INHIBITOR AND BEING SUFFICIENT TO DISPLACE SAID INHIBITOR FROM SAID INHIBITOR INJECTION SYSTEM AND FROM SAID INLET INTO SAID VAPOR SPACE. 